PCRAM cell manufacturing

ABSTRACT

An exemplary embodiment of the present invention includes a method for forming a programmable cell by forming an opening in a dielectric material to expose a portion of an underlying first conductive electrode, forming a recessed chalcogenide-metal ion material in the opening and forming a second conductive electrode overlying the dielectric material and the chalcogenide-metal ion material. A method for forming a recessed chalcogenide-metal ion material comprises forming a glass material to be recessed approximately 50% or less, in the opening in the dielectric material, forming a metal material on the glass material within the opening and diffusing metal ions from the metal material into the glass material by using ultraviolet light or ultraviolet light in combination with a heat treatment, to cause a resultant metal ion concentration in the glass material.

FIELD OF THE INVENTION

[0001] This invention relates to semiconductor fabrication processingand more particularly, to methods for forming programmable capacitordynamic random access memories (PCRAMs) utilizing a programmablemetallization cell.

BACKGROUND OF THE INVENTION

[0002] Memory devices are used in electronic systems and computers tostore information in the form of binary data. These memory devices maybe characterized as either volatile memory, where the stored data islost if the power source is disconnected or removed or non-volatile,where the stored data is retained even during power interruption. Anexample of a non-volatile memory device is the programmable conductorrandom access memory (PCRAM) that utilizes a programmable metallizationcell (PMC).

[0003] A PMC comprises a fast ion conductor such as a chalcogenide-metalion and at least two electrodes (e.g., an anode and a cathode)comprising an electrically conducting material and disposed at thesurface of the fast ion conductor a set distance apart from each other.When a voltage is applied to the anode and the cathode, a non-volatilemetal dendrite rapidly grows from the cathode along the surface of thefast ion conductor towards the anode. The growth rate of the dendrite isa function of the applied voltage and time; the growth of the dendritemay be stopped by removing the voltage or the dendrite may be retractedback towards the cathode, or even disintegrated, by reversing thevoltage polarity at the anode and cathode. Changes in the length andwidth of the dendrite affect the resistance and capacitance of the PMC.

[0004] One of the important elements of the PMC is the fast ionconductor, which plays a critical part during the programming of thePMC. The construction of the fast ion conductor is key to providingeffective and reliable programming of the PMC and is a significant focusof the present invention.

[0005] Thus, the present invention comprises fabrication techniques toform a programmable metallization cell, for use in a programmableconductor random access memory, that will become apparent to thoseskilled in the art from the following disclosure.

SUMMARY OF THE INVENTION

[0006] An exemplary embodiment of the present invention includes amethod for forming a programmable cell by forming an opening in adielectric material to expose a portion of an underlying firstconductive electrode, forming a recessed chalcogenide-metal ion materialin the opening and forming a second conductive electrode overlying thedielectric material and the chalcogenide-metal ion material.

[0007] A method for forming a recessed chalcogenide-metal ion materialcomprising forming a glass material being recessed approximately 50% orless, in the opening in the dielectric forming a metal material on theglass material and diffusing metal ions from the metal material into theglass material by using ultraviolet light or ultraviolet light incombination with a heat treatment, to cause a resultant metal ionconcentration in the glass material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a cross-sectional view depicting a semiconductorsubstrate covered with layers of silicon dioxide, tungsten, which formsthe first conductor of the programmable metallization cell, and siliconnitride.

[0009]FIG. 2 is a subsequent cross-sectional view taken from FIG. 1after patterning and etching a via into the silicon nitride to exposethe underlying tungsten.

[0010]FIG. 3 is a subsequent cross-sectional view taken from FIG. 2following the formation of a recessed germanium/selenium material intothe via.

[0011]FIG. 4 is a subsequent cross-sectional view taken from FIG. 3following the formation of a silver layer that overlies the siliconnitride and the recessed germanium/selenium material.

[0012]FIG. 5 is a subsequent cross-sectional view taken from FIG. 4following the planarization of the silver layer to the level of thesurface of the silicon nitride.

[0013]FIG. 6 is a subsequent cross-sectional view taken from FIG. 5following the formation of a planarized second conductive electrode forthe programmable metallization cell.

DETAILED DESCRIPTION OF THE INVENTION

[0014] An exemplary implementation of the present invention is directedto a process for forming a programmable metallization cell (PMC) for aPCRAM device as depicted in FIGS. 1-6.

[0015] The following exemplary implementation is in reference to thefabrication of programmable conductor random access memory (PCRAM)device. While the concepts of the present invention are conducive to thefabrication of PCRAMs, the concepts taught herein may be applied toother semiconductor devices that would likewise benefit from the use ofthe process disclosed herein. Therefore, the depiction of the presentinvention in reference to the manufacture of a PCRAM (the preferredembodiment), is not meant to so limit the extent to which one skilled inthe art might apply the concepts taught hereinafter.

[0016] Referring to FIG. 1, a semiconductive substrate 10, such as asilicon wafer, is prepared for the processing steps of the presentinvention. As described above, a PMC may be implemented in variousdifferent technologies. One such application is in memory devices.Insulating material 11, such as silicon dioxide, is formed oversubstrate 10. Next, conductive material 12, such as tungsten, is formedover insulating material 11. Conductive material 12 will function as oneof the conductive electrodes of the PMC. Next, dielectric material 13,such as silicon nitride, is formed over conductive material 12.

[0017] Referring now to FIG. 2, masking material 21 is patterned andthen followed by an etch to removed an unmasked portion of dielectricmaterial 13, with the etch stopping once it reaches conductive material12. This etch results in the formation of via (opening) 22 inpreparation for the subsequent formation of a chalcogenide-metal ionmaterial, such as metal ion laced glass material.

[0018] Referring now to FIG. 3, masking material 21 of FIG. 2 isstripped and glass material 31, such as Ge₃Se₇, is formed such as tosubstantially fill via 22. Glass material 31 is then planarized down tothe surface of dielectric material 13, by using an abrasiveplanarization etching technique, such as chemical mechanicalplanarization (CMP).

[0019] Referring now to FIG. 4, planarized glass material 31 is recessedwithin via 22, by using either a dry or wet etch. A specific, exemplarywet etch would incorporate the use of NH₄OH. A specific, exemplary dryetch would incorporate the use of a fluorine based chemistry, though anydry etch that will remove oxide would be effective. Regardless of thetype of etch used, it is desirable that glass material 31 is recessedwithin via 22 approximately 50% or less (ideally 40-50%) the depth ofopening 22, the importance of which will become apparent later in thedescription of the process.

[0020] Next, a metal material 41, such as silver, is formed overdielectric material 13 and recessed glass material 31. Other metalmaterials that may be used for metal material 41 include tellurium andcopper. Then, metal material 41 is either irradiated with ultravioletlight or thermally treated in combination with irradiation to causesufficient diffusion of metal ions from metal material 41 into recessedglass material 31. For example, metal material 41 may be irradiated for15 minutes at 4.5 mw/cm² with the ultraviolet light at 405 nmwavelength. Additionally, the irradiation may be used in combinationwith a thermal process using the settings of 110° C. for 5-10 minutes.The irradiation process is sufficient to cause the desired diffusion ofion metals; however, the disclosed thermal process by itself is not andthus must be used in combination with the irradiation process. It ispreferred that the resultant metal ion concentration in the glassmaterial be approximately 27%+/−10%, to ensure the formation of aconductive path/dendrite during the eventual programming of the PMC.

[0021] Referring now to FIG. 5, metal material 41 is planarized back tothe top surface of dielectric material 13, leaving a residual layer ofmetal material 41 on top of recessed glass material 31 (shown in FIG.4), which is now laced with metal ions to form a metal ion-laced glassmaterial 51. By recessing glass material 31 within via 22 by 40-50% in aprevious step, a sufficient amount of metal material 41 is guaranteed toremain after the metal material is planarized so that residual metalmaterial 41 provides an ample source of metal material for diffusion ofmetal ions into the glass material. Also, residual metal material 41must be thin enough to allow penetration of the ultraviolet light andthe metal ion laced glass material 51 must maintain sufficient thicknessin order to function properly as a fast ion conductor.

[0022] Referring now to FIG. 6, a second conductive electrode 61 isformed over dielectric material 13 and residual metal material 41 tocomplete the formation of the PMC. Suitable conductive materials thatcan be used to form electrode 61 include a conductive material that willeffectively alloy with the metal material selected to form metalmaterial 41, of which silver is preferred. In the case where silver isused to form conductive material 41, suitable conductive materials forelectrode 61 include tungsten, tantalum, titanium, tantalum nitride,tungsten nitride and so forth. The resulting structure forms a fast ionconductor comprising a chalcogenide-metal ion material (i.e., such asglass layer 51 containing a concentration of silver ions) and at leasttwo conductive electrodes, namely electrodes 12 and 61. The PCRAM isthen completed in accordance with fabrication steps used by thoseskilled in the art.

[0023] The PMC is programmed by applying a sufficient voltage acrosselectrodes 12 and 61 to cause the formation of a conductivepath/dendrite (or referred to simply as a dendrite) between the twoelectrodes 12 and 61, by virtue of a conductor (i.e., such as silver)that is now present in metal ion laced glass layer 51. In general terms,the dendrite can grow at any point on the cell starting with theelectrode that is opposite the excess metal. In the specific example ofthe present invention, with the programming voltage applied acrosselectrodes 12 and 61, the dendrite grows vertically at the surface offast ion conductive material 51 and along the inside of via 22, with thedendrite extending from electrode 12 towards electrode 61.

[0024] It is to be understood that, although the present invention hasbeen described with reference to a preferred embodiment, variousmodifications, known to those skilled in the art, may be made to thedisclosed process herein without departing from the invention as recitedin the several claims appended hereto.

What is claimed is:
 1. A method of forming a programmable cellcomprising the steps of: forming an opening in a dielectric material toexpose a portion of an underlying first conductive electrode; forming arecessed chalcogenide-metal ion material in said opening; and forming asecond conductive electrode overlying said dielectric material and saidrecessed chalcogenide-metal ion material.
 2. The method of claim 1,wherein said step of forming a recessed chalcogenide-metal ion materialcomprises the steps of: forming a glass material to be recessed in saidopening; forming a metal material on said glass material within saidopening; diffusing metal ions from said metal material into said glassmaterial.
 3. The method of claim 2, wherein said step of forming a glassmaterial to be recessed in said opening comprises forming a glassmaterial in said opening and subsequently removing approximately 50% orless of said glass material resident in said opening.
 4. The method ofclaim 2, wherein said step of forming a glass material to be recessed insaid opening comprises forming a glass material in said opening andsubsequently removing approximately 40-50% of said glass materialresident in said opening.
 5. The method of claim 2, wherein said step ofdiffusing metal ions comprises irradiating said metal material forapproximately 15 minutes at 4.5 mw/cm² with an ultraviolet light havinga 405 nm wavelength.
 6. The method of claim 5, further comprisesthermally heating said metal material at approximately 110° C. for 5-10minutes during said irradiating.
 7. The method of claim 2, wherein saidstep of diffusing metal ions comprises causing a resultant metal ionconcentration in said glass material to be approximately 27%+/−10%.
 8. Amethod of forming a programmable cell comprising the steps of: formingan opening in a dielectric material to expose a portion of an underlyingfirst conductive electrode; forming a glass material to be recessed insaid opening; forming a metal material on said glass material withinsaid opening; diffusing metal ions from said metal material into saidglass material; and forming a second conductive electrode overlying saiddielectric material and said metal material.
 9. The method of claim 8,wherein said step of forming a glass material to be recessed in saidopening comprises forming a glass material in said opening andsubsequently removing approximately 50% or less of said glass materialresident in said opening.
 10. The method of claim 8, wherein said stepof forming a glass material to be recessed in said opening comprisesforming a glass material in said opening and subsequently removingapproximately 40-50% of said glass material resident in said opening.11. The method of claim 8, wherein said step of diffusing metal ionscomprises irradiating said metal material for approximately 15 minutesat 4.5 mw/cm² with an ultraviolet light having a 405 nm wavelength. 12.The method of claim 11, further comprises thermally heating said metalmaterial at approximately 110° C. for 5-10 minutes during saidirradiating.
 13. The method of claim 8, wherein said step of diffusingmetal ions comprises causing a resultant metal ion concentration in saidglass material to be approximately 27%+/−10%.
 14. A method of forming aprogrammable capacitor dynamic random access memory comprising the stepsof: forming a first conductive electrode on a substrate surface; forminga dielectric material on said first conductive electrode; forming anopening in said dielectric material to expose a portion of said firstconductive electrode; forming a glass material to be recessed in saidopening; forming a metal material on said glass material within saidopening; diffusing metal ions from said metal material into said glassmaterial; and forming a second conductive electrode overlying saiddielectric material and said metal material.
 15. The method of claim 14,wherein said step of forming a glass material to be recessed in saidopening comprises forming a glass material to be recessed in saidopening and subsequently removing approximately 50% or less of saidglass material resident in said opening.
 16. The method of claim 14,wherein said step of forming a glass material to be recessed in saidopening comprises forming a glass material in said opening andsubsequently removing approximately 40-50% of said glass materialresident in said opening.
 17. The method of claim 16, wherein said stepof diffusing metal ions comprises irradiating said metal material forapproximately 15 minutes at 4.5 mw/cm² with an ultraviolet light havinga 405 nm wavelength.
 18. The method of claim 17, further comprisesthermally heating said metal material at approximately 110° C. for 5-10minutes during said irradiating.
 19. The method of claim 14, whereinsaid step of diffusing metal ions comprises causing a resultant metalion concentration in said glass material to be approximately 27%+/−10%.20. A method of forming a programmable capacitor dynamic random accessmemory comprising the steps of: forming a first conductive electrode ona substrate surface; forming a dielectric material on said firstconductive electrode; forming an opening in said dielectric material toexpose a portion of said first conductive electrode; forming a glassmaterial to be recessed by approximately 50% or less in said opening;forming a metal material on said glass material within said opening;diffusing metal ions from said metal material into said glass material;and forming a second conductive electrode overlying said dielectricmaterial and said metal material.
 21. The method of claim 20, whereinsaid step of forming a glass material to be recessed in said openingcomprises forming a glass material in said opening and subsequentlyremoving approximately 40-50% of said glass material resident in saidopening.
 22. The method of claim 20, wherein said step of diffusingmetal ions comprises irradiating said metal material for approximately15 minutes at 4.5 mw/cm² with an ultraviolet light having a 405 nmwavelength.
 23. The method of claim 22, further comprises thermallyheating said metal material at approximately 110° C. for 5-10 minutesduring said irradiating.
 24. The method of claim 20, wherein said stepof diffusing metal ions comprises causing a resultant metal ionconcentration in said glass material to be approximately 27%+/−10%. 25.A method of forming a programmable capacitor dynamic random accessmemory comprising the steps of: forming a first conductive electrode ona substrate surface; forming a dielectric material on said firstconductive electrode; forming an opening in said dielectric material toexpose a portion of said first conductive electrode; forming a glassmaterial to be recessed by approximately 50% or less in said opening;forming a silver based material on said glass material within saidopening; diffusing silver ions from said silver based material into saidglass material such that a resultant silver ion concentration in saidglass material is approximately 27%+/−10%; and forming a secondconductive electrode overlying said dielectric material and said metalmaterial.
 26. The method of claim 25, wherein said step of forming aglass material to be recessed in said opening comprises forming a glassmaterial in said opening and subsequently removing approximately 40-50%of said glass material resident in said opening.
 27. The method of claim25, wherein said step of diffusing metal ions comprises irradiating saidmetal material for approximately 15 minutes at 4.5 mw/cm² with anultraviolet light having a 405 mn wavelength.
 28. The method of claim27, further comprises thermally heating said metal material atapproximately 110° C. for 5-10 minutes during said irradiating.